FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10; rule 13)
TITLE OF THE INVENTION
"A Method of Improving the Brake Feel Of the Vehicle"


APPLICANTS
TATA MOTORS LIMITED, an Indian company
Having its registered office at Bombay House,
24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
INVENTORS
Mr. Rajesh A T and Mr. Badal G Bisen
AH Indian Nationals
of TATA MOTORS LIMITED,
An Indian company having its registered office
at Bombay House, 24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India

PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed.


FIELD OF INVENTION
This invention relates to brake system used in vehicles and more particularly relates to provision of brake liner having higher /improved brake factor in an identified window of operation to improve the overall brake feel of non booster type having drum - drum combination without pressure correction valve.
BACKGROUND OF INVENTION
The subject brake system in the invention consists of front drum -rear drum combination without booster and pressure correction valve. This is against the conventional brake system comprising of booster assisted front disc brake with pressure correction valve.
The function of the brake system is as mentioned. The master cylinder operated by brake pedal pressurizes the fluid and this pressurized fluid is transferred through the non compressible brake pipe and hoses to the front and rear wheel cylinder. The wheel cylinder expands the brake shoes fitted with the friction lining and the pressure in the system holds the shoe against the drum which retards the vehicle.
The brake performance characteristics include pedal force versus pedal travel, vehicle deceleration versus pedal force and vehicle deceleration versus pedal travel. Another important subjective characteristic is the Brake feel which is defined as the sensation transmitted to the driver during braking action via the brake pedal.
The major disadvantage in the performance characteristics of this type of brake system is poor brake pedal feel due to lack of linearity in the brake performance.
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This is mainly due to ineffective braking at lower pedal travel and lower line pressure.
United States Patent 5771773 discloses improving brake feel by using a combination of link mechanism and brake booster. The lever ratio is varied by a link mechanism while the rate of increase of output force is varied by the brake booster so as to obtain a linear relationship between pedal force and deceleration. However, this mechanism makes the braking system costly and it requires more space.
United States Patent 4007665 shows the use of a control valve to control fluid flow from pump to brake booster so as to vary brake feel in different operating conditions. Use of valves makes the system costly.
United States Patent 6309031 describes the use of various sensors and controller to vary pedal effort in different situations to provide improved brake feel. Outputs of pedal position sensor, steering position sensor and seat position sensor are fed to the controller and the braking system automatically adjusts the braking effort based on a sensed position signal. Use of sensors and controllers makes the braking system very costly. This system is unsuitable for entry-level vehicles where cost is at a premium.
OBJECTS OF INVENTION
The main object of the present invention is to provide an improved brake system for a vehicle.
Another object of the present invention is to provide an improved brake system for a vehicle which will be able to give a better brake pedal feel especially at lower speeds and lower pedal efforts.
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BRIEF DESCRIPTION OF INVENTION
The brake feel can be improved by increasing the brake factor of the brake liner at lower line pressure. This is achieved by jacking up the brake torque at lower line pressure and lower speed, keeping the overall high speed brake performance at normal level. This is turn is achieved by modifying the brake liner composition and construction so as to obtain the higher level of coefficient of friction at lower line pressure.
In accordance with this invention, The method of improving the brake feel of a vehicle comprising the step of: identifying the window of lower pedal travel and pedal force where the brake performance is poor at various vehicle speed. This can be identified by conducting a brake test and finding the deceleration achieved for a small pedal force and pedal travel; identifying the corresponding line pressure. This can be obtained form the force/pressure characteristics of the master cylinder or by having a pressure transducer in the brake line during the test; identifying the corresponding brake factor at that particular speed and line pressure. This can be identified from the liner characteristics curve; increase the brake factor of the brake liners at that particular window of operation. The brake factor can be increased by changing the characteristics of the friction material used for molding the liner; measuring of performance on dynamometer with simulated vehicle test cycle; confirmation through vehicle testing for the improvement in the performance with the brake liners having increased brake factor.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 shows the layout of the braking system. Fig. 2 shows the brake drum assembly. Fig. 3 shows the various stages in braking.
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Fig. 4 shows the graph of Pedal Effort Vs Brake factor characteristic
Fig. 5 shows the graph of Pedal Effort Vs Deceleration Characteristic at low
speed.
Fig. 6 shows the graph of Pedal Travel Vs Deceleration Characteristic at low
speed.
DETAILED DESCRIPTION OF INVENTION
Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting the same,
Now referring to figure -01, the brake system consists of brake pedal, master cylinder, brake fluid, hydraulic lines and the drum brake assembly. When the brake pedal (6) is pressed, it moves the brake piston in master cylinder (3) which pressurizes the fluid in the said cylinder. This pressure is transferred through the non compressible fluid in the brake lines (4). The fluid pushes against slave pistons which applies force to friction liners on the brake shoes in the front drum brakes (1 and 2) and the rear drum brakes (5 and 7).
Referring to figure-02, The Drum Brake assembly comprises; a brake drum which rotates with the wheel, two brake shoes (I) which are mounted on a stationary brake plate. The brake shoes are pivoted on one end (3) and connected to the actuator (5) at the other end. When the brakes are applied, the pressurized brake fluid acts on the pistons in the actuator (wheel cylinder) to push the brake shoes outward against the drum. The friction between the friction material on brake shoes and the brake drum creates a braking torque which slows down the vehicle. The return spring (4) pulls back the brake shoes away from the surface of the brake drum when the brakes are released.
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In accordance with the preset invention, Method of improving the brake feel of a vehicle comprising the step of:
Identifying the window of lower pedal travel and pedal force where the brake performance is poor at various vehicle speeds. This can be identified by conducting a brake test and finding the deceleration achieved for a small pedal force and pedal travel.
The corresponding line pressure is now identified. This can be obtained form the force/pressure characteristics of the master cylinder or by having a pressure transducer in the brake line during the test.
The corresponding brake factor at that particular speed and line pressure is now identified. This can be identified from the liner characteristics curve. The brake factor of the brake liners is now increased at that particular window of operation.
The brake factor can be increased by changing the characteristics of the friction material used for molding the liner.
The performance is measured on a dynamometer with simulated vehicle test cycle.
The result is confirmed through vehicle testing for the improvement in the performance with the brake liners having increased brake factor.
The line pressure is identified either by force pressure characteristic of master cylinder or by fixing the pressure transducer in the brake liner.
Now referring to Figure 5 which shows the relation between pedal effort and deceleration achieved for a particular vehicle speed. This characteristic is plotted
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by conducting a brake test on the vehicle at particular vehicle speed. The pedal effort is varied form minimum to the maximum and the deceleration achieved at various pedal efforts is noted.
Now referring to Figure 6 which shows the relation between pedal travel and deceleration achieved on the vehicle. This characteristic is plotted by conducting a brake test on the vehicle at particular vehicle speed. The pedal travel is varied form minimum to the maximum and the deceleration achieved at various pedal efforts is noted.
In order to achieve good brake feel, it is essential to achieve higher vehicle deceleration at lower pedal effort and lower pedal travel. Also the deceleration should be progressive with respect to pedal effort and pedal travel.
Figure 5 clearly shows that for the baseline brake liners, it required higher pedal effort to achieve smaller deceleration (approximately 13kg to achieve 3m/s2 of deceleration). Figure 6 shows that the pedal travel required to achieve smaller deceleration is also higher. These behaviors of the brake system will in turn reflect in poor pedal feel to the customer.
Figure-03 indicates that the vehicle brake performance during the initial stage of braking responsible for smaller deceleration is inferior leading to un-acceptable brake feel. Thus it is essential to improve the brake performance in the initial stage of braking to achieve an acceptable brake feel. This can be improved by jacking up the vehicle deceleration in the initial stage of braking. This will in turn improve the pedal effort/ deceleration characteristics and pedal travel/deceleration characteristics of the brake system on the vehicle.
To achieve the improved pedal effort, the brake factor of the brake liner is increased in the identified window which belongs to the initial stage of braking as
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shown in figure 4. The vehicle performance was mapped with the improved brake liners. The performance with the improved liners is aJso shown in figure 5 and 6. The graph shows increase in the deceleration at lower pedal travel and decrease in pedal effort to achieve the same deceleration. This in turn gives a better pedal feel to the driver.
The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof

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WE CLAIM
1. A method of improving the brake feel of a vehicle comprises the steps of:
identifying the window of lower pedal travel and pedal force;
identifying corresponding line pressure;
identifying corresponding brake factor at that particular speed and line pressure;
increasing the brake factor of brake liners at that particular window of operation;
measuring of performance on dynamometer with simulated vehicle test cycle; and
confirming through vehicle testing for the improvement in the performance with the brake liners having increased brake factor.
2. The method as claimed in claim 1 wherein said window is the initial stage of braking where brake performance is poor at various vehicle speed.
3. The method as claimed in claim 1 wherein said window of lower pedal travel is identified by finding the deceleration achieved for small pedal force and pedal travel after conducting the brake test.
4. The method as claimed in claim 1 wherein said line pressure is identified either by force pressure characteristic of master cylinder or by fixing the pressure transducer in the brake liner.
5. The method as claimed in claim 1 wherein said brake factor is identified form the liner characteristics curve.
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6. The method as claimed in claim 1 or 5, wherein the brake factor is increased by changing the characteristics of the friction material used for molding the brake liner.
7. A method of improving the brake feel of a vehicle as herein described substantially with reference to accompanying drawings.
8. An system for performing the methods as claimed in the preceding claims.
Dated this 11th day of November 2008
TATA MOTORS LIMITED By their Agent & Attorney

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(Karuna Goleria) of DePENNING & DePENNING